The invention relates to a method to attach brush bristle tufts onto carriers made of thermoplastic material, which are incorporated into brush bodies.
In order to produce brushes, brush bodies can be provided with a perforation pattern, corresponding to the desired tuft pattern. The bristle tufts are then inserted into the holes of the brush body and anchored in the holes. The anchoring of the bristle tufts in the brush body by means of anchor plates or loops, however, calls for very high-performance and thus complex machines.
According to an alternative brush manufacturing process, the bristle tufts are attached to a carrier that is then incorporated into a brush body, for example, during the injection molding process. The generally plate-shaped carrier is provided with holes corresponding to the desired perforation pattern. The bristle tufts are inserted into the holes, whereby the tips of the bristle tufts that are to be used protrude from one surface of the carrier while the axial ends of the bristle tufts that are to be anchored in the brush protrude slightly from the opposite side. These ends of the bristle tufts that are to be anchored in the brush body are then heated, fused together and shaped into a knob.
In order to ensure adequate axial anchoring of the bristle tufts in the carriers, DE 197 38 256 C2 has proposed providing the plate-like carriers with mushroom-shaped projections which are enclosed from below by the melted material of the bristles, so that the mushroom-shaped projections and the plastically deformed mass of the bristle tufts become interlocked. This process, however, calls for a great deal of work in order to provide the plate-shaped carrier with a multiplicity of mushroom-shaped projections.
The invention provides a method of attaching brush bristle tufts to carriers made of thermoplastic material by means of which extremely simple method steps ensure a firm anchoring of the bristle ends in the carriers. According to the invention, a heated punch with projections penetrates between the holes into the mass of the carrier, softening it and pushing it laterally into the interstices of the bristle tufts. In this process, first of all, the material of the carrier is softened and deformed so that it tightly encircles the ends of the bristle tufts and, by penetrating into the interstices between the bristles, creates a tight interlocking fit. In the preferred embodiment of the method, the surface of the punch that is between the projections is then pressed against the axial ends of the bristle tufts, whereby the displaced mass of the bristles extends over the deformed mass of the carrier. Thus, a tight interlock is created between the carriers and the bristle tufts. Here, the projections encircle the axial ends of the bristle tufts and give the melted plastic compound a precisely defined shape. During this method, the bristle tufts are preferably held or supported axially so that they are not shifted axially in the holes of the carrier.
The invention also provides a device for executing the process which is characterized by a heatable punch with a working surface that has multiple projections arranged relative to the tuft insertion holes in the carrier.